单选题在某些昆虫的幼虫中，多线染色体产生的原因是：______。 A.一条染色体发生断裂，与同一条染色体的另一部位重新连接 B.在染色体复制之前，细胞分裂发生了几次 C.染色体发生了复制，但没有发生相对应的核分裂 D.在进行非等位交换时，一条染色体的一小部分发生了复制

单选题除了达尔文之外，另一个人提出了与自然选择相同的学说，是推动进化学的主要力量，他把自己的学说告诉了达尔文，促使达尔文的“物种起源”学说的传播。这个人是谁?( )

单选题小麦为异源六倍体作物，其x=7。所以他的单体系列可以有______种类型。 A．42 B．28 C．21 D．7

单选题玉米n+1花粉不育，n+1胚囊则可育。已知R产生红色，r无色。在杂交RRr♀×rr♂中子代的表现型比例是______。 A．1红色:1无色 B．3红色:1无色 C．5红色:1无色 D．6红色:1无色

单选题很相似但不同种的鱼把卵细胞和精子排放在同一水域中，其中一种鱼的精子不能进入另一种鱼的卵细胞内。这是由于下列哪种原因所引起的?( )

单选题The cultured E. coli system was infected by two types of bacteriophages. One type is a-b-, another is a+b+. Then the lysate was sampled and smeared on medium. The data of the bacteriophage growth by counting plaques is as follows: a+b+=4750, a+b-=370, a-b+=330, a-b-=4550. How much is the recombination rate between a and b? ______ A．70% B．12.8% C．7% D．15%

单选题让Hfr arg- leu+ azis strr与F- arg+ leu- azir strs混合培养，使其发生接合，想增多F-重组型arg+ leu+ azir的出现，下面哪一种培养基将完成这个选择?______。 A．具有str的基本培养基 B．具有azi的基本培养基 C．具有leu和azi的培养基 D．具有str azi的基本培养基

单选题When two of the world's richest and mightiest men pledge to destroy an enemy, it is time to pay attention. Bill Gates, the former boss of Microsoft who now devotes all his time to his charitable foundation, travelled this week to New York, the city run by Michael Bloomberg, to join his fellow billionaire's campaign to stamp out smoking. Have the two potentates met their match? Despite decades of work by health campaigners, more than one billion people still smoke today. Smoking kills up to half of those who fail to quit puffing, reducing their lives by an average of 10 to 15 years. The World Health Organisation (WHO) says more than 5 million people a year die early from the effects (direct or indirect) of tobacco. That exceeds the combined toll of HIV/AIDS, tuberculosis and malaria. Despite that dismal situation, there are three reasons to give the latest pair of campaigners a slim chance of success: money, methods and motivation. Messrs Gates and Bloomberg vowed to spend a combined total of $ 500 million on discouraging the weed. Since Mr. Bloomberg's charity had already announced an award of $125 million earlier, the new money pledged this week totalled a "mere" $ 375 million: $ 250 million from the mayor, and a fresh $ 125 million from the software magnate's philanthropic outfit. How will this cash be spent? In quite innovative ways, and that is a second reason for optimism. Hitherto, most anti-smoking funds have been channelled through a few large bureaucracies. But Mr. Bloomberg's charity wants to let a thousand flowers bloom: in other words, to lend a hand to many initiatives, both public and private, to see what works. There will be a competitive grant scheme for poor countries where the tobacco habit is spreading. The very fact that two giants are teaming up is a landmark in American philanthropy- comparable to Warren Buffett's decision, two years ago, to put his fortune at the disposal of Mr. Gates' foundation. As part of their joint commitment, Mr. Gates is giving some of his $ 125 million directly to Mr. Bloomberg's charity; the rest will go to carefully monitored projects in India, China and other places where the number of smokers is rising relentlessly. Then there is motivation. There are other big players in this cause, and that should induce every new entrant to try bringing something fresh to the party. Earlier this year the WHO started a campaign against tobacco known as MPower. One of its selling points was that in contrast with many other projects, it had a fairly clear idea about what was needed. WHO experts have listed a series of tactics, ranging from aggressive public education to a rise in tobacco taxes, that deliver results. (Even if high taxes lead to some smuggling and diversion, studies done in Brazil, for example, show that fiscal measures do curb consumption. ) The World Bank, which funded that research, is also thought to be ready to join the anti-smoking scrum after years of paying little attention. A crowded field, indeed. But having an extra $ 500 million from two hard-driven billionaires surely won't hurt.

单选题以病毒颗粒为载体将遗传物质从一个细胞转移到另一个细胞的过程称为 ____ 。

单选题入噬菌体侵入大肠杆菌细胞后通过( )而进入溶源状态。

单选题对达尔文自然选择学说的正确评价是( )。

单选题下列有关种群的叙述中，不正确的是( )。

单选题家猫中，如果一个决定条纹毛色的常染色体显性基因外显不全，但其表现度稳定，下面的描述哪句正确______

单选题A female-male mosaic fruit fly may be formed, if there is chromosome loss or______． A．equal division during sperm generation B．abnormal mitosis during merogenesis(fertilized egg cleavage) C．meiosis in embryo D．meiosis when sperm is tailed

单选题转导过程中产生的转导子，下面哪种说法对转导子的描述是正确的?( )

单选题白猫与黑猫交配，F1都是白猫。F1相互交配，F2中白、黑、棕三种小猫的比例是12:3:1。这是什么原因引起的?______ A．显性上位作用 B．抑制作用 C．突变 D．环境影响

单选题转化时，供体菌a+b+c+可给受体菌a-b-c-提供DNA，假定这些基因是紧密连锁的，顺序为abc，它们很容易一起遗传，那么下列何种转化类型出现的最少______ A．a-b+c- B．a+b-c+ C．a+b+c+ D．a-b+c+ E．由于三个位点可能在同一片段上传递，故各类转化类型出现的频率相等。

单选题在Hfr×F-杂交中，染色体转移的起点决定于( )。

单选题假设用两种噬菌体(一种是a-b-，另一种是a+b+)感染E.coli，然后取其裂解液涂布培养基，得到以下结果a+b+=4750，a+b-=370，a-b+=330，a-b-=4550，从这些资料看，a和b间的重组率多大?______ A.70% B.12.8% C.7% D.15% E.上述答案均不对

单选题E.coli F + ad + str s ×ad - str r 两种杂交，预期的菌株将在下列哪种培养基上被选择出来(ad是腺嘌呤的缩写)?______